The invention relates to a method for producing aromatic carboxylic acids by oxidizing aromatic hydrocarbons which have alkyl substituents or partially oxidized alkyl substituents.
Aromatic carboxylic acids are one of the important basic chemicals, and are especially useful as raw materials for the production of fibers, resins or plasticizers. By way of examples, terephthalic acid is in wide use as a raw material for the production of polyesters and its demand is recently increasing.
Aromatic carboxylic acids are produced usually by a method in which methyl substituted aromatic hydrocarbons are oxidized by a molecular oxygen containing gas in the presence of a catalyst comprising a heavy metal salt and a bromine compound in an organic solvent such as a lower aliphatic carboxylic acid, for example, acetic acid, in a reactor. However, according to the method, the molecular oxygen containing gas is blown into the liquid phase in which the reaction is carried out so that the liquid phase foams and the volume efficiency of the reactor is small, and hence the method has a problen that the productivity is low.